This invention relates generally to detecting when an object moves in an oil or gas well. In a particular application, the invention relates to electronically indicating when a cementing plug has been displaced out of a plug container.
One method of detecting when a cementing plug has left the plug container includes using a mechanical flipper mechanism. The flipper extends out into the plug container below the plug. When the plug is released and drops or is displaced downward, it contacts the flipper, causing the flipper to rotate downward into a slot machined in the plug container. The flipper is connected to a shaft, which moves with the flipper. An indicator is attached to one end of the shaft on the outside of the plug container. This indicator moves with the shaft and the flipper, giving an external indication that the cementing plug has moved past the flipper.
There are shortcomings with this flipper-type indicator. If it is not cleaned periodically, the flipper becomes cemented in place. This renders it useless if it is in the slot, and this prevents the cementing plug from being displaced down the casing if the flipper is cemented in the extended position.
Electronic methods of indicating when the plug has left the plug container would not have the aforementioned mechanical shortcoming of becoming cemented; however, I am not aware of a commercially successful electronic method for detecting displacement of a cementing plug.
From the foregoing, there is still the need for an improved apparatus and method for indicating when an object moves in an oil or gas well. This is specifically applicable to determining whether a cementing plug has displaced from its plug container. There is also the need for an improved object, including a cementing plug, which enables such detection to occur.
The present invention overcomes the above-noted and other shortcomings of the prior art by providing a novel and improved apparatus and method for detecting an object moving in a conduit of an oil or gas well. The present invention also provides a novel and improved object which can be displaced in an oil or gas well and which enables the displacement to be detected.
One embodiment of the object to be displaced in an oil or gas well as provided by the present invention comprises a body movable through a conduit of an oil or gas well and an electrical circuit connected to the body, wherein the electrical circuit is responsive to an externally generated alternating current electromagnetic signal such that the electrical circuit transmits a responsive signal for reception outside the object as the object moves through the conduit. The object can also be defined to comprise a body movable through a conduit of an oil or gas well and an active or passive radio frequency identification tag electrical circuit connected to the body.
Detector apparatus for an oil or gas well as provided by the present invention generally comprises: a body movable through a conduit of an oil or gas well; an electrical circuit connected to the body, the electrical circuit for transmitting an electromagnetic signal for reception away from the body as the body moves through the conduit; and a receiver disposed relative to the conduit and the body to receive the electromagnetic signal from the electrical circuit. In particular implementations, the body is selected from the group consisting of a movable plug, ball and dart. The receiver can include an antenna mounted through the conduit. The detector apparatus can further comprise a transmitter disposed relative to the conduit and the body to transmit into the conduit an alternating current electromagnetic signal, wherein the electrical circuit transmits its electromagnetic signal in response to the alternating current electromagnetic signal from the transmitter.
The present invention also provides a method of detecting an object moving in a conduit of an oil or gas well. The method comprises: providing a triggering electromagnetic signal from outside an object moving in a conduit of an oil or gas well; generating, from an electrical circuit on the object moving in the conduit responding to the triggering electromagnetic signal, a responsive electromagnetic signal; and detecting the responsive electromagnetic signal away from the moving object.
The present invention can also be defined as a method of detecting a plug moving in a plug container of an oil or gas well, comprising: generating an electromagnetic signal from an electrical circuit on the plug moving in the plug container; and detecting the electromagnetic signal away from the moving plug.